package hDOJ;

/*
吐了
2*1 ==> 1
2*2 ==> 2
2*3 ==> 3
2*4 ==> 5
2*5 ==> 8


 */



import java.util.Scanner;

public class Main2046 {
    
    public static void main(String[] args) {
        
        Scanner sc = new Scanner(System.in);
        while(sc.hasNext()) {
            int n = sc.nextInt();
            long[] f = new long[51];
            f[0] = 1;
            f[1] = 2;
            f[2] = 3;
            for(int i = 3; i < n; i++) {
                f[i] = f[i-1] + f[i-2];
            }System.out.println(f[n-1]);
        }
    }
}
